An endoscope is an elongated tubular structure which is inserted into body cavities to examine them. The endoscope includes a telescope with an objective lens at its distal end. The telescope includes an image-forwarding system. In rigid endoscopes it is a series of spaced-apart lenses. In flexible endoscopes it is a bundle of tiny optical fibers assembled coherently to forward the image. This invention is applicable to both types of image forwarding systems.
At the proximal end of the image-forwarding system is an ocular lens which creates a virtual image for direct human visualization. Often a camera means such as a CCD chip, is mounted to the endoscope. It receives the image and produces a signal for a video display.
While surgeons can, and often do, look directly into the endoscope through an ocular lens, it is more common for them to use an attached video camera and observe an image on a video screen. In a surgical or diagnostic procedure, the surgeon manipulates the endoscope. He may tilt it, push it in, pull it out, and also rotate it around its mechanical axis. As these manipulations occur to an endoscope with an attached CCD camera, the camera faithfully relates what it sees, with its own upright axis displayed as the upright axis of the image on the display. This means that if the camera is rigidly fixed to the endoscope, then as the endoscope-camera is rotated around its mechanical axis, the displayed image on the monitor will move proportionately and in the opposite direction as the endoscope-camera. A clockwise rotation of the endoscope-camera through an angle of 45 degrees will cause a counterclockwise rotation of the image on the monitor through an angle of 45 degrees.
That is the very problem. When the image is displayed on the screen and the endoscope is rotated around its axis, it is as though the surgeon must tilt his head to follow it. However, the surgeon is standing up, and the rotating image is distracting to him. What he really wants to see on the screen is an image that is oriented the same as he would see it if he were inside, standing up, with the same upright orientation. Stated otherwise, he would prefer to see what he would see if he were looking directly into the endoscope, instead of viewing a screen. This is impossible when the camera is fixed to the telescope and rotates with it, while the surgeon does not.
In a conventional endoscope and camera arrangement, the camera is usually detachably and rotably connected to the endoscope. In this arrangement the rotated image on the monitor screen can be righted by manually counter-rotating only the camera such that its orientation is upright. Alternatively, one can avoid this rotated image condition by holding the camera in its upright position and rotating only the endoscope.
Suggestions have been made to decouple the camera from the telescope so the camera can rotate independently of it, using a pendulum to seek the vertical. This seemingly sensible approach runs afoul of conditions imposed by the use of the instrument. Endoscopes are used in close quarters, and their proximal ends must be kept as small and uncluttered as possible. Physical interference with surroundings and with the surgeon's hands must be eliminated or greatly minimized. However, a pendulum to be useful must have a substantial mass and a substantial arc to work through, requiring enlargement of the instrument. Furthermore, when the endoscope is tilted, the axis of rotation of the pendulum is no longer horizontal. Now there must be bearings to support the pendulum, and the component of the force of gravity acting on the pendulum is reduced. Even worse, when the slope is very steep, a mechanical pendulum may not receive a sufficient force to seek the vertical.
Sometimes, however, there may be reasons to attach the endoscope such that it cannot rotate with respect to the camera. Or, alternatively, it may be desirable to embed the CCD camera within the endoscope housing. In these circumstances it is not possible to manually rotate the camera with respect to the endoscope, so some other means is necessary to right the displayed image. Furthermore it is desirable to have this image rotation occur automatically so that, regardless of the physical orientation of the endoscope-camera in space, the displayed image of an object will always be correctly oriented with respect to the viewer's reference frame.
Rotation of the image by electronic manipulation would appear to be a useful solution. However, it runs afoul of the aspect ratio of the camera and of its display. Such rotation can eliminate from the display information located near corners and edges of the viewed field which might be of interest to the surgeon. This problem can be visualized by rotating a photograph in a picture frame. Also, this requires exotic and expensive attitude sensing devices.
It is an object of this invention to maintain the rotary position of the CCD image sensing device so that its upright axis lies in a vertical plane with respect to the viewer utilizing an accelerometer responsive to gravity, a servo mechanism responsive to its signal, and a servo motor to rotate the CCD sensing device.